The need to communicate telephonically is an endemic part of modern society. Communication of voice, as well as other, data is effectuated by way of telephonic communication systems.
Telephonic communications are effectuable, for instance, by way of a wireless communication system. A wireless communication system advantageously obviates the need of wireline connections to interconnect the communication stations between which data is to be communicated. The use of a wireless communication system is advantageous, for example, when the use of a conventional, wireline communication system would be inconvenient or impractical. And, the installation costs associated with the installation of a radio communication system are generally less than the costs required to install the infrastructure of a wireline communication system.
A cellular communication system is an exemplary radio communication system. Telephonic communications are effectuable by way of a cellular communication system. Cellular communication systems have been installed throughout significant parts of the populated portions of the world, and use of cellular communication systems to communicate telephonically therethrough have achieved wide levels of usage. Various cellular communication standards have been promulgated, setting forth the operational parameters of different types of cellular communication systems. Successive generations of communication-system standards have been promulgated.
In a cellular communication system, a fixed network infrastructure is installed throughout a geographical area. Mobile stations positioned within the geographical area are generally able to communicate with the network infrastructure. The fixed network infrastructure includes fixed-site, base transceiver stations with which a mobile station communicates. Each base transceiver station defines an area, referred to as a cell, from which the cellular communication system derives its name.
A mobile station, also formed of a transceiver, is usually of dimensions to permit its carriage by a user. Use of the cellular communication system is permitted, typically, pursuant to a service subscription. And, a user, referred to as a subscriber, communicates by way of the cellular communication system through utilization of a mobile station.
Because radio channels are utilized to interconnect a base transceiver station and a mobile station, oscillators are utilized at the respective transceivers to convert data that is to be communicated during operation of the communication station upon the radio channels. Relative frequency drift of the oscillators of the respective transceivers, both short-term and long-term drift, cause the respective transceivers to operate at frequencies offset to one another. Frequency control schemes, including automatic frequency controls (AFC) schemes, have been developed and are regularly utilized in many different types of radio communication systems. Some frequency control schemes use a feed-back control mechanism by which to maintain the oscillators of the separate communication stations in frequency synchronization with one another. Other frequency control schemes form open-loop schemes that compensate for the relative frequency offsets.
Technical advancements in communication technologies have permitted the development of modulation schemes that utilize higher-density constellations, sampled at higher sampling rates. The need to maintain frequency control between communication stations, such as a base transceiver station and a mobile station, is of even greater significance because of the higher-density constellation that is used and the higher sampling rate at which received data is sampled. Greater channel dispersion occurs, and increasingly complex detection problems result. Relative, time-varying frequency offsets between the communication stations result in relative constellation rotations of the constellation sets from which the symbols forming the data that is communicated are members. And, such frequency offset degrades the ability of a receiving station correctly to recover the informational content of the communicated data.
The computing complexity of some existing frequency control schemes quickly become impractical as the number of symbols used to compute frequency offset increases. For instance, maximum likelihood estimation (MLE), frequency offset algorithms are used to compute roots of a likelihood polynomial to obtain frequency offset values.
In an exemplary cellular communication system operable pursuant to a GSM/EDGE (global system for mobile communication/enhanced data for GSM evolution) provides for the generation as transmission of training symbol bursts. Conventional MLE root-computation operations to determine the roots of a likelihood polynomial responsive to reception of such training sequences is impractically difficult to compute at the required sampling rates. Therefore, an improved manner by which to facilitate estimation of frequency offsets between communication stations operable in a communication system, such as a cellular communication system operable pursuant to a GSM/EDGE operational protocol, is needed.
It is in light of this background information related to frequency control in a communication system that the significant improvements of the present invention have evolved.